Very little of what we directly observe overlaps except our interaction with each other, and this was all I was talking about.
If I was to quantify your 'very little' I'd guess you mean say < 1% observational overlap.
Lets look at the rough storage cost first. Ignoring variable data priority through selective attention for the moment, the data resolution needs for a simulated earth can be related to photons incident on the retina and decreases with an inverse square law from the observer.
We can make a 2D simplification and use google earth as an example. If there was just one 'real' observer, you'd need full data fidelity for the surface area that observer would experience up close during his/her lifetime, and this cost dominates. Let's say that's S, S ~ 100 km^2.
Simulating an entire planet, the data cost is roughly fixed or capped - at 5x10^8 km^2.
So in this model simulating an entire earth with 5 billion people will have a base cost of 5x10^8 km^2, and simulating 5 billion worlds separately will have a cost of 5x10^9 * S.
So unless S is pathetically small (actually less than human visual distance), this implies a large extra cost to the solipsist approach. From my rough estimate of S the solipsist approach is 1,000 times more expensive. This also assumes that humans are randomly distributed, which of course is unrealistic. In reality human populations are tightly clustered which further increases the relative gain of shared simulation.
However, one thing you may very much desire would be reunification with former loved ones, dead ancestors, and so on [...] So once you have enough computational power, I suspect there will be a desire to use it in an attempt to resurrect the dead.
I think this is evil, but I'm not willing to say whether the future intelligences will agree or care.
Evil?
Why?
Most importantly, you're assuming that all circuitry performs computation, which is clearly impossible.
I'm not sure what you mean by this. Does all of the circuitry of the brain perform computation? Over time, yes. The most efficient brain simulations will of course be emulations - circuits that are very similar to the brain but built on much smaller scales on a new substrate.
That leaves us to debate about how much of it can, but personally I see no reason that the computational minimum cost will closely (even in an exponential sense) be approached
My main reference for the ultimate limits is Seth Lloyd's "Ultimate Physical Limits of Computation". The Singularity is Near discusses much of this as well of course (but he mainly uses the more misleading ops per second, which is much less well defined).
Biological circuits switch at 10^3 to 10^4 bits flips/second. Our computers went from around that speed in WWII to the current speed plateau of around 10^9 bit flips/second reached early this century. The theoretical limit for regular molecular matter is around 10^15 bit flips/second. (A black hole could reach a much much higher speed limit, as discussed in Lloyd's paper). There are experimental circuits that currently approach 10^12 bit flips/second.
In terms of density, we went from about 1 bit / kg around WWII to roughly 10^13 bits / kg today. The brain is about 10^15 bits / kg, so we will soon surpass it in circuit density. The juncture we are approaching (brain density) is about half-way to the maximum of 10^30 bits/kg. This has been analyzed extensively in the hardware community and it looks like we will approach these limits as well sometime this century. It is entirely practical to store 1 bit (or more) per molecule.
Lastly, but most importantly (to me), how strongly do you personally believe that a) you are a simulation and that b) all entities on Earth are full-featured simulations as well?
A and B are closely correlated. Its difficult to quantify my belief in A, but it's probably greater than 50%.
I've thought a little about your last question but I don't yet even see a route to estimating it. Such questions will probably require a more advanced understanding of simulation.
If there was just one 'real' observer, you'd need full data fidelity for the surface area that observer would experience up close during his/her lifetime, and this cost dominates. Let's say that's S, S ~ 100 km^2.
I feel like this would make you a terrible video game designer :-P. Why should we bother simulating things in full fidelity, all the time, just because they will eventually be seen? The only full-fidelity simulation we should need is the stuff being directly examined. Much rougher algorithms should suffice for things not being directly observed...
Many folk here on LW take the simulation argument (in its more general forms) seriously. Many others take Singularitarianism1 seriously. Still others take Tegmark cosmology (and related big universe hypotheses) seriously. But then I see them proceed to self-describe as atheist (instead of omnitheist, theist, deist, having a predictive distribution over states of religious belief, et cetera), and many tend to be overtly dismissive of theism. Is this signalling cultural affiliation, an attempt to communicate a point estimate, or what?
I am especially confused that the theism/atheism debate is considered a closed question on Less Wrong. Eliezer's reformulations of the Problem of Evil in terms of Fun Theory provided a fresh look at theodicy, but I do not find those arguments conclusive. A look at Luke Muehlhauser's blog surprised me; the arguments against theism are just not nearly as convincing as I'd been brought up to believe2, nor nearly convincing enough to cause what I saw as massive overconfidence on the part of most atheists, aspiring rationalists or no.
It may be that theism is in the class of hypotheses that we have yet to develop a strong enough practice of rationality to handle, even if the hypothesis has non-negligible probability given our best understanding of the evidence. We are becoming adept at wielding Occam's razor, but it may be that we are still too foolhardy to wield Solomonoff's lightsaber Tegmark's Black Blade of Disaster without chopping off our own arm. The literature on cognitive biases gives us every reason to believe we are poorly equipped to reason about infinite cosmology, decision theory, the motives of superintelligences, or our place in the universe.
Due to these considerations, it is unclear if we should go ahead doing the equivalent of philosoraptorizing amidst these poorly asked questions so far outside the realm of science. This is not the sort of domain where one should tread if one is feeling insecure in one's sanity, and it is possible that no one should tread here. Human philosophers are probably not as good at philosophy as hypothetical Friendly AI philosophers (though we've seen in the cases of decision theory and utility functions that not everything can be left for the AI to solve). I don't want to stress your epistemology too much, since it's not like your immortal soul3 matters very much. Does it?
Added: By theism I do not mean the hypothesis that Jehovah created the universe. (Well, mostly.) I am talking about the possibility of agenty processes in general creating this universe, as opposed to impersonal math-like processes like cosmological natural selection.
Added: The answer to the question raised by the post is "Yes, theism is wrong, and we don't have good words for the thing that looks a lot like theism but has less unfortunate connotations, but we do know that calling it theism would be stupid." As to whether this universe gets most of its reality fluid from agenty creators... perhaps we will come back to that argument on a day with less distracting terminology on the table.
1 Of either the 'AI-go-FOOM' or 'someday we'll be able to do lots of brain emulations' variety.
2 I was never a theist, and only recently began to question some old assumptions about the likelihood of various Creators. This perhaps either lends credibility to my interest, or lends credibility to the idea that I'm insane.
3 Or the set of things that would have been translated to Archimedes by the Chronophone as the equivalent of an immortal soul (id est, whatever concept ends up being actually significant).